Cellularized light metal



May 3, 1960 J. F. PASHAK CELLULARIZED LIGHT METAL Filed March 7. 1957 I N V EN TOR. John E Pasha/r W #Ma HT 7' ORNE Y8 .Ufli s m Perm Q 2,935,396 CELLULARIZED LIGHT METAL John F. Pashak, Linwood, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application March 7, 1957, Serial No. 644,608

. 8 Claims. (Cl. 75 -20) Theinvention relates to cellularized light metal, such as magnesium and the magnesium-base alloys and alumitruth and the aluminum-base alloys. It more particularly concerns a method by which the metal is given a cellular structure having lightness and strength.

Insofar as I am aware, no method is commercially available by which cellularized articles of the light metals magnesium, aluminum and the alloys having these metals as a base may be produced without melting. Accordingly, it is the principal object of the invention to provide a method fulfilling this need.

I The invention is based upon the discovery that'by ad mixing a carbonate of one of the second group metals cadmium, magnesium, with a suitable particulate solid form of the metal to be cellularized, die expressing the mixture at a temperature at which the metal particles undergo a welding together during the die expression, and

then heat treatingthe die expressed product at a temfor stiffening purposes, by suitably heat treating the die expressed product placed within the object.

The invention then consists of the method of cellularizing the aforesaid light metal herein fully described and particularly pointed out in the claims, the annexed drawing illustrating an embodiment of'the invention.

If desired, the cellu- 'lar product can be formed in situ in hollow. objects,'as

"ice

2 a a a a finely divided state, for example, in particles smaller than about 50 microns. A preferred range of size is from 0.1 to 0.3 micron. V 1 1 The particulated metal and pulverulent carbonate are mixed together in suitable proportions whereby to at least partially coat the metal particles with carbonate particles which are dust like and more or less adhere to the metal particles. The amount of carbonate to use is not sharply critical and may range from about 0.5 to 20 percent of the weight of the metal, a preferred amount being about 5 percent in the case of a carbonate of magnesium or 15 percent in the case of cadmium carbonate. Generally satisfactory results are had with from about 2 to 8 percent of magnesium carbonate, for example; 'MiXr ing can be etfected in various ways, as for example, by tumbling the metal and carbonate particles together in a closed vessel, such as a barrel which is turned end over end. Mixing, in which the particles are tumbled about in a vessel revolving at 50 r.p.m., can be accomplished satisfactorily in 15 minutes but other mixing times ma be used.

The mixture of metal and carbonate particles is changed into the container of an extrusion press and die. expressed at a temperature somewhat lower, e.g. 25 to 350 Fahrenheit degrees lower, than that which would .be suitable for the extrusion of the metal alone-as under stood in the metal extrusion art. In the case of magnesium-base alloys, for example, the temperature of thechargein the container may be as low as 300 F. Itis desirable to avoid extrusion temperatures at which excessive composition of the carbonate occurs, and for 'this reason; it is preferable to extrude the charge at as low a'temperature as practicable without incurring the use of excessive pressures which tend to produce excessive wear on the extrusion dies and other parts of the extrusionapparatus. Satisfactory extrusion results can 'be obtained over a wide range of temperature as for example 400 to 850 F. The extrusion or die expressing operation welds the metal particles together into a rigid body consisting of a matrix of metal in which the carbonate particlesjariedis} persed as more or less discrete-masses enveloped-in'the 1 In the drawing the single figure is a fragmentary view breadth, and. thickness does not exceed 10 times any other.' Usable metal particles are those which pass through a No. 10 standard sieve and of which not more than 10 percent pass through aNo. 325 mesh standard sieve. Preferred particles have a size such as'to pass through a No. 20 standard sieve with not more than 10 percent passing through a No. 100 standard sieve. An

,7 assortment of sizes of particle is desirable, uniformity of size preferably is to be avoided. 1 Various carbonates of the aforesaid second group metal 'may be used in pulverulent form, for example: magnesite (MgCO nesquehonite (MgCO .3H O), hydromagnesite (3MgCO .Mg(OH) .3H O), lansfordite aniline", (MgCO .Mg(OH) .3H O), cadmium carbonate KCdCO Of these the heavy basic carbonate, hydromagnesiteis preferred. These materials'are normally-of metal.

The die expressed product so-obtained is heat treated at a sufficiently elevated temperature to bring aboutlelea'jse of gas from the carbonate in the interstices of the metal matrix thus bringing about gas bubble formation, ltlicitfmperature being high enough to permit plastic deformation of the metal whereby the gas generated produces expansion of the metal matrix into a cellular form. t

The cellular product so-obtained has a lower-density than that of the metal of which it is formed, theireductio'ri' in density depending upon the nature ofthecarbonate, metal, and operating conditions particularly the temperature of the die expression and heat treating steps. The cell size in general ranges from 0.01 .to 20 mm. in diameter with the majority of them in size .range of0.03 to 1.0 mm. in diameter. In the case of magnesium; base alloys, such as those containing up to 6 percent of zinc with =0I"Wltl10lli up to 6 percent of aluminum, and up to 0.8 percent of dissolved zirconium, except in alloys containing aluminum, the balance being magnesium, the density may range from about 0.5 to 1.1 grams per cc. and compressive strengths of from about 1800 to 4500 p.s.i. may be obtained with tensile strengths of 1800 to 2100 p.s.i. Shear strengths may range from 2000 to: 4000 p.s.i. and impact strength, by the Charpy test, from 0.25 to 0.60 foot pound. In addition 'to-the desirable properties of lightness in weight coupled with strength, the cellularized product strongly holds nails and screws. For example, in cellularized magnesium-base alloy, a 10 penny nailrequires a pull of 157 pounds per inch of penetration for withdrawal. This may be j 7 1 pared to a withdrawal pull of 132 pounds per inch and 70 pounds per inch of penetration of the same nail in yellow pine and white pine, respectively, perpendicular to the grain. A 1 /2 inch No. 10 wood screw requires a pull of 1200 pounds for withdrawal per inch of penetration into cellularized magnesium-base alloy. In comparison the withdrawal pull of a similar screw from white pine is 320 pounds per inch of penetration. The cellularized product formed in accordance with the invention possesses an unusually low thermal conductivity being, in the case of magnesium-base alloy, about to of that of the alloy itself.

Referring to the figure in the drawing, the alloy cellularized had the nominal composition of 6 percent zinc, 0.6 percent zirconium, balance magnesium. The alloy was in the form of more or less spherical particles most .of which passed through a 10 mesh sieve and were retained on a 100 mesh sieve. The particles were mixed with percent by Weight of hydromagnesite having a specific gravity of 2.16. Mixing was efiected by placing the metal and carbonate particles in a tumbling barrel for 30 minutes. The resulting mixture was charged into a 4 inch diameter cylindrical container of an ext'rusion press fitted with a die having a 1 inch diameter opening. The charge was heated to about 440 F. and the die to about 430 F. From 450 to 500 tons push was applied to the ram of the press, thereby die expressing the mixture into a 1 inch diameter bar. This was then heat treated for 0.5 hour at 960 F. as a result of which the bar became cellularized with the structure shown and its density was 0.71 gram per cc.

The following tabulated data are illustrative of operating conditions and densities obtainable in practicing the invention.

the die expressed object then expands in situ filling the mold cavity thereby taking the configuration of the mold cavity surface.

As used in the specification and claims, the terms aluminum-base alloy and magnesium-base alloy means alloys of these metals in which the aluminum and the magnesium respectively eonstitut eat least 80 percent or the weight of the alloy.

I claim:

1. The method of producing a cellularized form of a light metal selected from the group consisting of aluminum, magnesium and the alloys having one of these metals as a base which comprises commingling particles of the metal and a particulated carbonate of a metal selected from the group consisting of cadmium and magnesium in the proportions of from 0.5 to 15 percent of the weight of the metal particles, die expressing the soformed mixture at a temperature of 25 to 350 Fahrenheit degrees lower than a temperature suitable for die expressing the metal alone, and then heat treating the soobtained product at a temperature and for a time sufiicient to decompose the carbonate therein thereby to generate gas in situ causing the product to become cellularized.

2. The method according to claim 1 in which the light metal is a magnesium-base alloy.

3. The method according to claim 1 in which the light metal is an aluminum-base alloy.

4. The method according to claim 2 in which the particulated carbonate is nesquehonite.

5. The method according to claim 2 in which the particulated carbonate is cadmium carbonate.

6. The method according to claim 2 in which the carbonate is hydromagnesite.

Table Composition of Mix Extrusion Heat Treatment Example Product No. Density,

Alloy Composition Particle Carbo- Per- Temp., Redue- Time, Temp., Gram/cc.

Size 1 nate cent F. tion Hours F.

20 +100 OdCOs 10 700 0:1 0.25 1050 1.1 20 +100 CdCOa 15 700 9:1 1. 0 960 0.78 10 +10 MgCos 5 500 9:1 0. 5 960 0.68 10 +100 higC Os 5 440 9:1 0. 5 980 0. 57 100 MgC O3 5 360 9: 1 0.5 960 0. 82 10 +100 MgCOz 5 400 36:1 0.5 960 0.73 10 +100 MgCOs 1 400 0.5 960 0.83 20 MgCOa 5 400 9:1 0.25 1000 0. 85 20 MgCOa 5 400 9:1 1. 0 1000 1! 0. 9 20 MgCOa 5 400 9:1 1.0 1000 2 1. 0 20 MgC 0a 5 650 31:1 0. 5 980 2.14 1.?i)%1l\gig, 0.25% Cr, 0.7% Si, 20 MgCO; 5 625 31:1 0.5 980 1.86

8. 1.6% Cu, 2.5% Mg, 0.3% Cr, 20 MgOOa 5 625 31:1 0.5 980 1. 43

5.6% Zn, bal. Al.

i 1 The minus sign followed by a number means that the particles pass thru a standard sieve or that number; plus sign followed by a number means that the particles are retained on a standard sieve of that number.

9 Estimates.

Nos. 1-11, inc., metal particles substantially spherical, formed by atomizing.

Nos. 12 and 13 metal particles are sawdust. MgC 0a is nesquehonite.

Reduction is the ratio of the cross-sectional area of the extrusion press container compared to the area of the die opening.

In using the cellularized product as a filling, as for example, for stifiening a hollow article, the die expressed product before heat treatment may be given a shape having the configuration of but smaller size than the hollow to be filled. The size of the shaped die expressed product to be used as a filling can be calculated from the density change expected on submitting the die expressed product to heat treatment. The so-shaped and sized die expressed product is placed in the space to be filled and then heat treated in situ to effect the desired expansion and cellularization. If desired, the cellularized product can be shaped by forming it in situ in a die or mold cavity having the form desired. In this case, as in filling a hollow object, the die expressed product before heat treatment, and somewhat smaller in volume than the mold cavity, is placed in the mold cavity and heat treated in situ. As a result of the heat treatment, 75 2,784,125

References Cited in the file of this patent UNITED STATES PATENTS 2,434,775 Sosnick Jan. 20, 1948 2,464,517 Kuntz Mar. 15, 1949 2,517,223 Mantell Aug. 1, 1950 2,553,016 Sosnick May 15, 1951 2,659,137 Leontis et a1. Nov. 17, 1953 2,671,955 Grubel et a1. Mar. 16, 1954 2,721,378 Oliver et a1 Oct. 25, 1955 2,751,289 Elliott June 19, 1956 la ke Ma 195.1 

1. THE METHOD OF PRODUCING A CELLULARIZED FORM OF A LIGHT METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM AND THE ALLOYS HAVING ONE OF THESE METALS AS A BASE WHICH COMPRISES COMMINGLING PARTICLES OF THE METAL AND A PARTICULATED CARBONATE OF A METAL SELECTED FROM THE GROUP CONSISTING OF CADMIUM AND MAGNESIUM IN THE PROPORTIONS OF FROM 0.5 TO 15 PERCENT OF THE WEIGHT OF THE METAL PARTICLES, DIE EXPRESSING THE SOFORMED MIXTURE AT A TEMPERATURE OF 25 TO 350 FAHRENHEIT DEGREES LOWER THAN A TEMPERATURE SUITABLE FOR DIE EXPRESSING THE METAL ALONE, AND THEN HEAT TREATING THE SOOBTAINED PRODUCT AT A TEMPERATURE AND FOR A TIME SUFFICIENT TO DECOMPOSE THE CARBONATE THEREIN THEREBY TO GENERATE GAS IN SITU CAUSING THE PRODUCT TO BECOME CELLULARIZED. 